This invention relates to a novel process for resolving sludge/emulsion formed as a result of oil and gas well acidization, and a process for treating the resulting produced water to improve water quality sufficiently to allow water disposal offshore. More particularly, the invention relates to a method for removing soluble and insoluble organic material from aqueous fluids produced from subterranean formations during flowback after acid stimulation treatments to meet overboard water quality requirements of 29 ppm total oil and grease. The method comprises treating separated water from acid returns with a water clarifier and allowing the clarified water to separate from the skimmings in a settling vessel. The water from this vessel is further processed through a prefilter to remove any solids or residual free oil and then is treated by filtration through a macroreticular resin media to remove soluble organic material originating from the stimulation package. The cleaned water is then disposed of by pumping it into an overboard disposal line.
Periodically oil and gas wells are cleared of calcium carbonate buildup and other debris by a process called acidizing. When a well is acidized, production is shut down and acid is flushed under pressure through the well and into the reservoir. After acidizing is complete and production recommences, spent acid may come back up through the well and cause the formation of sludge/emulsion. Sludge/emulsion formation may be minimal on initial flowback, but as production fluids mix downhole with spent acid, additional sludge/emulsion may be formed. Sludge/emulsion formation may also occur when this acid flowback is commingled with the production from other wells.
Crude oil dehydration treating systems are typically used to reduce the basic silt, sediment, and water (BS&W) of crude oil to a certain acceptable level specified by a crude oil purchaser, typically a pipeline company. The level of BS&W typically specified by purchasers is less than 1%. A typical crude oil dehydration treating system is includes a separator, free water knockout, heater treater or chemelectric, and/or air flotation unit, etc. Such systems are well known in the art.
If a sludge/emulsion problem is not resolved promptly, it will cause a malfunction in the crude oil dehydration treating system. This type of malfunction is commonly referred to as a system upset. When a system upset occurs in the treating system, the required BS&W level cannot be achieved to meet a purchaser's specifications. Additionally, high levels of oil and other organic material will remain in the waste water from the system which prevents the waste water from meeting water quality specifications for release at sea. The chemicals and systems used for normal oil water separation and processing are not adequate to resolve the sludge/emulsion formed from acidizing oil and gas wells.
To date, the typical method of coping with the possibility of a system upset is to mechanically remove the sludge/emulsion by catching it in large storage tanks. Removal and treatment of sludge/emulsion is a major operational cost for producers. This is particularly true for offshore wells because the sludge/emulsion must be collected, stored, and transported to shore for treatment and disposal.
Conventional methods of removing sludge/emulsion formation include neutralizing acid flowback by raising the pH of the production fluid and subsequently adding emulsion breakers or other related chemicals. Problems exist with conventional sludge/emulsion treatment. The process is slow and the resulting produced water contains such a high oil content that it cannot be discharged due to environmental concerns.
There is a need for an efficient process to resolve the sludge/emulsion formed when acidizing oil/gas wells and to clean the resulting waste water sufficient to meet environmental regulations for discharging. The present invention meets this need.